Water-cooled grid structure



April 3, 1962 F. v. sAMs WATER-COOLED GRID STRUCTURE 4 Sheets-Sheet 1 Filed Nov. 28, 1960 FIG.

INVENTOR. FRE D V- SAMS BY WMM A TI'ORNEVS April 3, 1962 F. v. SAMS 3,027,881

WATER-COOLED GRID STRUCTURE Filed Nov. 28, 1960 4 Sheets-Sheet 2 INVENTOR.

Fred M. Sams Buc/rharn, Cheat/7am, a B/ore ATTORNEYS April 3, 1962 F. v. sAMs WATER-COOLED GRID STRUCTURE 4 Sheets-Sheet 3 Filed Nov. 28, 1960 INVENTOR.

Fred V. Sums Buck/70m, Chen/ham, 8 BIare ATTORNEYS April 3, 1962 Filed Nov. 28, 1960 F. v. SAMS WATER-COOLED GRID STRUCTURE 4 Sheets-Sheet 4 IN VEN TOR.

Fred Sums Buckhorn, Cheofhcrm 8 Blore ATTORNEYS United States Patent Ofifiee 3,927,831 Petented Apr. 3, 1952 3,027,881 WATER-CGULED GRID STRUCTURE Fred V. Same, 29% SW. Fairview Blvd,

Portland, Greg. Fiied Nov. 28, 1950, Ser. No. 72,005 15 illairns. (Cl. 122-373) This invention relates to grid structures for furnaces and also to grid structures for heat generators. This application incorporates the subject matter and is a continuation-impart of my prior copending application, Serial No. 818,748, filed June 8, 1959, entitled Water-Cooled Grid Structure and now abandoned. The just-mentioned application incorporates the subject matter and is a continuation-impart of my prior copending application, Serial No. 532,453, filed September 6, 1955, entitled Water- Cooled Grate Bar and now abandoned.

A main object of the present invention is to provide a grate bar having its end portions so formed that an assemblage of such bars will provide winding air passages therebetween instead of straight air passages, as is common in the prior art, thus better to hold and retain fuel on the fuel supporting surfaces of the assemblage.

Another object of the invention is to provide a grate bar formed so that it may be laid in a bed of grate bars without regard to end disposition of the bar, thus to lessen the time necessary to assemble the bars into a bed.

A further object of the present invention is to provide a grate bar having a clamp device for clamping it onto a pair of supporting pipes, the clamp device being so constructed as to restrain the said grate bar from shifting movement along the pipes against substantial forces.

A still further object of the invention is to provide a grate bar equipped with a pipe clamp which is so connected to the bar as to permit the bar to be formed narrower than heretofore possible, thus to achieve the advantages of better heat transfer to the bar supporting pipes and to increase the percentage of air space in a bed of such bars.

Another important object of the invention is to provide a heat generator for use in connection with a refuse burner for supplying heated fluid to a body to be heated, such as, for instance, a body of water in a log pond, or a boiler, or to radiators to heat the interior of a building, or to a kiln.

The bar of the present invention is characterized by having at least one, and preferably two, oblique end faces so that an assemblage of such bars will provide a winding passage at the ends of such bars to prevent slivers of fuel from readily dropping therebetween as occurs with straight air passage spaces. The bar is also characterized by being of identical configuration when viewed in plan regardless of its end-for-end disposition, so that it may be laid in a bed of bars without regard to such disposition. The bar is further characterized by being connected or mounted on a pair of pipes by means including a narrow headed bolt which permits the grate to be made narrower than heretofore possible. The clamping device is further characterized by having edge portions which are clamped in tight engagement across the supporting pipes to hold the bar against shifting movement along the pipes.

Various other objects of the present invention will be apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a fragmentary horizontal section of a boiler furnace showing a water-cooled grate made up of bars of the present invention;

FIG. 2 is a view taken in the direction of the arrows 2-2 of FIG. 1, showing the side faces of certain of the grate bars;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2, showing the end faces of certain of the grate bars;

FIG. 4 is a view taken along line 4-4 of FIG. 1, showing the end faces of certain of the grate bars;

FIG. 5 is a sectional view taken along line 55 of FIG. 1, showing the construction of a clamping bolt;

FIG. 6 is a schematic view in elevation of a heat generator embodying the concepts of the present invention;

FIG. 7 is a view of a modified form of heat generator;

FIG. 8 is an enlarged view of a heat generating system, parts broken away for convenience in illustration;

9 is an elevational view of the grid structure with only a few of the bars being mounted in place;

FIG. 10 is a horizontal section taken along line 10-10 of FIG. 9;

FIG. 11 is an enlarged fragmentary view of a portion of FIG. 9;

FIG. 12 is a sectional view taken along line 12-42 of FIG. 11;

FIG. 13 is a plan view of a further form of heat generator;

FIG. 14 is a vertical section taken along line 1414 of FIG. 13; and

FIG. 15 is a vertical fragmentary section through the slab recess.

Referring to the accompanying drawings, FIG. 1 shows a part of a boiler furnace including walls 11 and 13, wall 11 providing a ledge 15 (FIG. 3). A water preheating arrangement is provided for the furnace and includes a pipe system having a number of pairs of pipes, three pairs 17, 19 and 21 being shown. The pipes are connected in conventional fashion by return bend fittings 25, three of which are shown, to provide a continuous flow passage for the circulation of water beneath the grate of the furnace. The return bend fittings 25 are supported by the ledge 15, as shown in FEGS. 1 and 3. The pipes are also supported by a number of pipe supports 29, one of which is shown, which extend across the furnace and are mount ed on the furnace walls. The pipes are supported on the supports by means of struts 30.

The grate of the furnace comprises an assemblage or bed of grate bars which includes a row of identical side bars 31 for each side of the grate, and rows of identical intermediate bars 33. Each bar is clamped onto one pair of pipes by means of a bolt 35 and a clamp member 37 (FIG. 2), about which more will presently be said. The space between the bars adjacent the ledge 15 is filled in with a layer of chrome ore or settable material 39 which covers the return bend sections 25 and prevents the loss of fuel between such grate bars and the ledge 15.

Each of the grate bars 33 comprises an elongated block having a flat, upper, fuel supporting surface, two unduiated side faces defined by alternating projections 55 and recesses 53, and parallel end faces 49 and 51 which are arranged obliquely with reference to the length of the said block. The projections on one side of a block 33 are aligned in a direction transversely of the bar with the recesses on the other side. The projections are also equally spaced from one another and there are an equal number of projections on each side of the block.

The oblique end faces 49 and 51 are parallel and meet the side faces of a block at recessed portions of said side faces so that the diagonally opposed corners of the block are of identical configuration, thus permitting the block to be laid in a bed of blocks without regard to its end-for-end disposition. To state it another way, the opposite end portions of a bar 33 are of identical configuration but reversed from one another so that the bars are reversible end-for-end. I have discovered that a bar of the present type will have the reversibility characteristic provided it has a length exceeding a multiple of the distance between two projections by substantially one-half such distance and provided its end faces are parallel. It is pointed out that each bar 33 meets these conditions by having a length slightly less than four and one-half times the distance between two projections 55 and by having parallel end faces 49 and 51.

The side bars 31 are generally similar to intermediate bars 33 except that each bar 31 has an end face 58 which is normal to the length of its block, and one face 59 which is oblique to the length of the block. This facilitates positioning the ends 58 in close proximity to the inner surface of wall 13 to prevent loss of fuel between the ends of the grate bars 31 and such wall. Bars 31 are not reversible end-for-end without change of configuration as are bars 33.

The bottom surface of each of blocks 31 and 33 is defined by beveled end marginal surfaces 61 (FIG. 2) and beveled side marginal surfaces 53 (FIG. 3), and a central fiat surface 65 generally parallel to the fuel supporting surface of such block. Each block is also formed on its bottom surface with a pair of transverse, laterally spaced, semicircular recesses 69 for cooperatively fitting on a pair of pipes.

Clamping members 37 and bolts 35, previously mentioned, clamp the bars on the pipes in proper positions, such as shown in FIG. 1, with the projections and recesses being arranged in interdigitated relation to provide narrow winding air spaces between the side faces of the bars. Also, the oblique end faces of the bars provide narrow winding air passages which prevent loss of fuel.

Each bolt 35 has a narrow T-head (FIG. 5) of a width substantially equal to the diameter of the shank of the bolt but of a greater length. The head 74 is cooperatively received within a narrow recess 75 formed longitudinally in the fuel supporting surface of a grate bar, and the bolt shank is cooperatively received within a bore provided through the bar and centrally intersecting the recess 75.

The provision of narrow heads 7 4 and narrow recesses 75 permits the bars to be made very narrow, which is advantageous in that a larger percentage of air space in a bed of bars is provided, and heat transfer from the bars to the pipe is greater than it would be were the bars wider.

Each clamping member 37 assumes the form of a bar having a central hole through which the associated bolt 35 extends. A nut 77 threads onto the bolt and up against the bottom surface of the clamping member 37. Each clamping member is provided with curved recessed portions 81 at its ends for cooperatively fitting onto a pair of spaced water pipes. Each clamping member is also centrally relieved at 83 longitudinally thereof to provide spaced edge portions 85 which are clamped into tight engagement with the pipes firmly to hold the associated bar against shifting movement along the pipes. Thus the original spacing of the grate bars is maintained.

It is pointed out that the bars of one row may be shifted relative to the bars of an adjacent row to vary the size of the air spaces between the ends of the bars, because of the oblique configuration of such ends. It is further evident that by shifting the grate bars of a row relatively toward or away from one another, the size of the air spaces between the side faces of such bars may be either increased or decreased.

Referring to FIG. 6, a standard refuse burner 101 is shown as having the usual screen type dome 103 and is disposed next to a log pond 105. A sawmill, now shown, is conventionally located adjacent the pond and burner, and the sawdust and scrap products produced during the manufacture of lumber is fed from the mill to the burner, such as by means of a chute or conveyor 107 shown in FIG. 8. conventionally, the waste material is dumped into a pile in the center of the burner and eventually is consumed by the burning process. The

intense heat created by the burning products causes rapid deterioration of the walls of the furnace, and in addition, all the heat produced by the combustion process goes up the stack.

In the present invention, a heat generator in the form of a water-cooled grid structure, generally entitled 111, is disposed centrally of the burner 101 as shown in FIG. 8, and water is supplied to the grid structure through a pipe 113 and is discharged from the grid structure in a heated condition through a pipe 115. The pipes 113 and 115 are located in a tunnel 116 which terminates in a pit 117 formed beneath the grid structures. The pipes 113 and 115 may lead to a coil 119 as shown in FIG. 6, located in the pond 105 to keep the pond from freezing, or the pipes may lead to a boiler shed 121 as shown in FIG. 7, or to other heat using means.

Referring to FIGS. 8 through 12, the construction of the grid structure is more clearly shown. The grid structure comprises a plurality of vertical water pipes 151 connected by U-bend pieces 153 in a manner to provide for the flow of water from one pipe into the adjacent pipe and from the adjacent pipe into the next adjacent pipe. However, instead of circulating the water through all the pipes, beginning with the first and ending with the last, the pipes are arranged in sets of eight, in the particular form of the invention shown, and are connected by connecting pipes 155 to a supply manifold pipe 157, and by connecting pipes 159 to a discharge manifold pipe 161. The manifold pipes 157 and 161 form extensions of the supply and discharge pipes 113 and 115, respectively.

As is clearly shown in FIG. 10, the pipes are arranged in a circle and as is evident from F168. 8 and 9, the pipes are equipped with bars 31a which are identical to bars 31, except for spacing lugs or elements 165 formed on certain of the projections of the bars to assure a minimum spacing of the bars with respect to one another in a vertical direction.

The bars 31a are mounted on the pipes 151 in a manner somewhat similar to the manner in which the bars 31a are mounted on the pipes in FIG. 1. That is to say, as shown in FIG. 11, the bars 31a are arranged in longitudinal rows, and each bar is connected to two pipes by its clamping member 37, as is clearly shown in FIG. 12. However, the bars of one row are staggered or offset with respect to the bars of an adjacent row so that while a bar in one row is connected to two pipes, the two laterally adjacent bars in an adjacent row are each connected to one only of such two pipes. This not only holds the pipes in desired spaced relation with respect to one another, but also connects the various sets or sections of pipe to one another. Thus the pipes and bars may be considered as mutually supporting one another.

conventionally, the U-bend pieces 153 would be welded to the pipes 151. That is to say, that is the manner in which the U-bend pieces would normally be connected to the pipes 151. To hold the pipes in the desired positions, a few of the bars 31a may be connected to the pipes, the bars serving to hold the pipes in the desired spaced relationship so that the bars are held parallel to one another during the welding operation.

Referring to FIGS. 8 and 9 a hollow tubular support or pedestal 171 has the lower end thereof fixed in the floor of the pit 117 in any suitable manner. The upper end of the pedestal supports a conical hat, cap or shield 173 which directs falling refuse into an annular pile around the grid structure. Preferably the margin of the hat is scalloped to conform to the upper U-bend pieces 153 to assure that the margin of the shield will be closely disposed relative to the upper row of bars to prevent ingress of refuse into the interior of the grid structure and also to prevent undue escape of air at the location of the margin, it being contemplated that air under pressure may be supplied to the interior of the grid structure through the tunnel 116 and the pit 117.

FIGS. 13, 14 and 15 show a modified form of the in-- vention in which the heat generator or grid structure is mounted on a concrete slab 201 having a raised circular portion 203. The grid structure comprises a plurality of vertical regularly spaced pipes 205 connected by return bend members 207 so that water entering an inlet pipe 209 flows through the pipes 205 and eventually out through an outlet pipe 211. A recess 213 (FIG. 15 is provided in the raised circular portion 203 to accommodate the pipes 209 and 211.

A lower inner ring 215 of right angle cross section is bolted to the raised portion 203 and locates the lower ends of the pipes 205. An upper inner ring 217 locates the upper ends of the pipes. Clamps secure the rings to the pipes.

Certain pairs of the pipes 205 instead of being connected by simple return bend members 207 have upwardly and inwardly extending pipe portions 219, the upper ends of which are connected by return bend portions 221. These pipe portions are in heat transfer relation to a cap structure which includes a frusto-conical cap piece 223 and a cap cover 225. J-bolts 227 secure the return bend members 221 to the cap cover and thus the pipe portions 219 and the cap cover provide a rigid supporting structure. The cap cover is large enough so that when removed, a man may enter the heat generator for inspection, repair, etc. If desired, the frusto-conical cap piece 223 can be formed of several pieces (for instance, four) instead of a single piece, with the individual pieces secured by J-bolts or clips to the pipe portions 219.

The pipes 205 are connected by a plurality of bars 231 arranged in the same staggered pattern as shown in FIGS. 9 and 11 so that proper regular spacing of the pipes is assured and mutual support is provided.

Air is supplied to the interior of the structure by a duct 233.

If desired, a second pair of inlet and outlet pipes could be provided opposite pipes 209 and 211 so that the water would travel 180 instead of 360.

In connection with the bars 231, it is pointed out that the bars could be curved so as to conform at least generally to the circle of the pipes. If so, the surface exposed to burning products would be convex. However, the pipes could surround a Zone of burning products, with the bars on the inside of the pipes. If the bars were curved, the surface of a bar exposed to the burning products would be concave. It is further pointed out that while the exposed surface is shown of smooth contour, it could be wavy or irregular to increase heat transfer.

Having described the invention in what is considered to be the preferred embodiment thereof, it is desired that it be understood that the invention is not to be limited other than by the provisions of the following claims.

I claim:

1. A grate comprising a plurality of pairs of water pipes extending parallel to one another and supported in a common plane, a set of grate bars for each pair of pipes, said grate bars being elongated in a direction at right angles to the length of the pipe, said bars being arranged relative to the pipes to define longitudinal rows of bars in which the length of a bar is parallel to its row, and also to define transverse rows of bars in which the length of a bar is transverse to its transverse row, each bar having end faces and undulated side faces and a top surface exposed to the fuel, each undulated side face being defined by alternating projections and recesses of generally complementary configuration so that the projections on one bar may fit in interdigitated relation with respect to the projections on an adjacent bar, the projections on one side face of a bar being aligned with the recesses on the other side face of such bar considered in a direction transverse to the length of such bar, the end faces of at least certain of the bars being parallel and extending obliquely with respect to the length of the bar and meeting the side faces at recessed portions thereof thus to facilitate laying said bars in a bed without regard to the end-for-end disposition thereof, mounting means for each bar for engaging a pair of pipes and holding a bar in a fixed predetermined position in a direction parallel to the length of the bar so that the projections on a bar inherently are arranged in interdigitated relation with respect to the projections on an adjacent bar by merely mounting the bars on the pipes in adjacent relationship and without regard to end-for-end disposition thereof, said pipes being regularly spaced so that the end faces of the bars in a longitudinal row are disposed next to one another and the projections of the bars considered in such direction are regularly spaced, the opposite end faces of a bar together forming only an interrupted or partial continuation of the configuration of the projections and recesses of the bar so that there is a slot provided between the opposed end faces of a pair of bars when the bars are aligned in a direction parallel to the longitudinal row containing such bars, said mounting means providing for independent adjustment of each bar so that the slots between the end faces of the bars may be decreased or increased by misaligning the bars of a longitudinal row in echelon fashion, and the spaces between adjacent projections and recesses of the bars may be independently regulated by shifting a longitudinal row of bars in unison at a direction parallel to the length of the pipes and relative to an adjacent longitudinal row of bars.

2. A grate structure comprising a plurality of pairs of water pipes extending parallel to one another and forming a series of pipes, a set of grate bars for each pair of pipes, said grate bars being elongated in a direction at right angles to the length of the pipe, said bars being arranged relative to the pipes to define longitudinal rows of bars in which the length of a bar is parallel to its row, and also to define transverse rows of bars in which the length of a bar is transverse to its transverse row, each bar having end faces and undulated side faces and a top surface exposed to the fuel, each undulated side face being defined by alternating projections and recesses of generally complementary configuration so that the projections on one bar may fit in interdigitated relation with respect to the projections on an adjacent bar, the projections on one side face of a bar being aligned with the recesses on the other side face of such bar considered in a direction transverse to the length of such bar, the end faces of at least certain of the bars being parallel and extending obliquely with respect to the length of the bar and meeting the side faces at recessed portions thereof thus to facilitate laying said bars in a bed without regard to the end-for-end disposition thereof, mounting means for each bar for engaging a pair of pipes and holding a bar in a fixed predetermined position in a direction parallel to the length of the bar so that the projections on a bar inherently are arranged in interdigitated relation with respect to the projections on an adjacent bar by merely mounting the bars on the pipes in adjacent relationship and without regard to end-for-end disposition thereof, said pipes being regmlarly spaced so that the end faces of the bars in a longitudinal row are disposed next to one another and the projections of the bars considered in such direction are regularly spaced, said mounting means providing for independent adjustment of each bar along its pipes so that the spacing between the end faces of the bars may be varied by misaligning the bars of a longitudinal row in echelon fashion, and the spaces between adjacent projections and recesses of the bars may be independently regulated by shifting a longitudinal row of bars in unison in a direction parallel to the length of the pipes and relative to an adjacent longitudinal row of bars.

3. A grate structure comprising a plurality of pairs of water pipes extending parallel to one another and forming a series of pipes, a set of grate bars for each pair of pipes, said grate bars being elongated in a direction at right angles to the length of the pipe, said bars being arranged relative to the pipes to define longitudinal rows of bars in which the length of a bar is parallel to its row, and also to define transverse rows of bars in which the length of a bar is transverse to its transverse row, each bar having end faces and undulated side faces and a top surface exposed to the fuel, each undulated side face being defined by alternating projections and recesses of generally complementary configuration so that the projections on one bar may fit in interdigitated relation with respect to the projections on an adjacent bar, the projections on one side face of a bar being aligned with the recesses on the other side face of such bar considered in a direction transverse to the length of such bar, the end faces of at least certain of the bars being parallel and extending obliquely with respect to the length of the bar and meeting the side faces at recessed portions thereof thus to facilitate laying said bars in a bed without regard to the end-for-end disposition thereof, mounting means for each bar for engaging a pair of pipes and holding a bar in a fixed predetermined position in a direction parallel to the length of the bar so that the projections on a bar inherently are arranged in interdigitated relation with respect to the projections on an adjacent bar by merely mounting the bars on the pipes in adjacent relationship and without regard to end-for-end disposition thereof, said pipes being regularly spaced so that the end faces of the bars in a longitudinal row are disposed next to one another and the projections of the bars considered in such direction are regularly spaced, the opposite end faces of a bar together forming only an interrupted or partial continuation of the configuration of the projections and recesses of the bar so that there is a slot provided between the opposed end faces of a pair of bars when the bars are aligned in a direction parallel to the longitudinal row containing such bars.

4. A grid structure for facing burning products comprising a plurality of pairs of water pipes extending parallel to one another and forming a series of pipes, a set of bars for each pair of pipes, said bars being elongated in a direction at right angles to the length of the pipes, said bars being arranged relative to the pipes to define longitudinal rows of bars in which the length of a bar is parallel to its row, and also to define transverse rows of bars in which the length of a bar is transverse to its transverse row, each bar having end faces and undulated side faces and a surface exposed to the burning products, each undulated side face being defined by alternating projections and recesses of generally complementary configuration so that the projections on one bar may fit in interdigitated relation with respect to the projections on an adjacent bar, the projections on one side face of a bar being aligned with the recesses on the other side face of such bar considered in a direction transverse to the length of such bar, the end faces of at least certain of the bars being parallel and extending obliquely with respect to the length of the bar and meeting the side faces at recessed portions thereof thus to facilitate laying said bars in a bed without regard to the end-for-end disposition thereof, mounting means for each bar for engaging a pair of pipes and holding a bar in fixed predetermined position in a direction parallel to the length of the bar so that the projections on a bar inherently are arranged in interdigitated relation with respect to the projections on an adjacent bar by merely mounting the bars on the pipes in adjacent relationship and without regard to the end-for-end disposition thereof, said pipes being regularly spaced so that the end faces of the bars in a longitudinal row are disposed next to one another and the projections of the bars considered in such direction are regularly spaced, said mounting means including a clamp member to engage the opposite sides of a pair of pipes from that side engaged by the associated bar, said clamp member including edge portions transversely arranged relative to the associated pipes and forced against such pipes to resist movement of the bar longitudinally of such pipes.

5. A grid structure for facing burning products comprising a plurality of fluid-carrying pipes extending parallel to one another and forming a series of pipes, a plurality of elongated bars for said pipes, means mounting said bars on said pipes with each bar being connected to two pipes and with the length of the bars transverse to the pipes and with the bars arranged in longitudinally extending rows in which the length of a bar is parallel to its row, any two pipes having at least certain of the bars mounted solely thereon with such bars being aligned with one another in a direction longitudinally of such pipes, each bar having end faces and undulated side faces and a surface exposed to the burning products, each undulated side face being defined by alternating projections and recesses of generally complementary configuration so that the projections of one bar may fit in interdigitated relation with respect to the projections on a laterally adjacent bar, the projections on one side face of a bar being aligned with recesses on the other side face of such bar considered in a direction transverse to the length of such bar, at least certain of the bars each having its end faces parallel to one another and extending obliquely with re spect to the length of such bar and meeting the side faces at recessed portions thereof thus to facilitate mounting said bars on said pipes without regard to the end-for-end disposition thereof, said mounting means holding each bar on its pipes in a fixed predetermined position in a direction parallel to the length of such bar so that the projections on a bar inherently are arranged in interdigitated relation with respect to the projections on a laterally adjacent bar by merely mounting the bars on the pipes in adjacent relationship and without regard to the end-forend disposition thereof, said pipes being regularly spaced so that the end faces of the bars in a longitudinal row are disposed next to one another and the projections of the bars considered in such direction are regularly spaced.

6. A grid structure as set forth in claim 5 in which said mounting means includes a clamp member for each bar to engage the opposite sides of a pair of pipes from that side engaged by the associated bar, said clamp member including edge portions transversely arranged relative to the associated pipes and forced against such pipes to resist movement of the bar longitudinally of such pipes.

7. A grid structure as set forth in claim 5 in which said mounting means provides for independent adjustment of each bar along its pipes so that the spacing between the end faces of the bars may be varied by misaligning the bars of a longitudinal row in echelon relation, and the spaces between adjacent projections and recesses of the bars may be independently regulated by shifting a longitudinal row of bars in unison in a direction parallel to the length of the pipes and relative to an adjacent longitudinal row of bars.

8. A grid structure as set forth in claim 5 in which the opposite end faces of a bar together forming only an interrupted or partial continuation of the configuration of the projections and recesses of the bar so that there is a slot provided between the opposed end faces of the pair of bars when the bars are aligned in a direction parallel to the longitudinal row containing such bars.

9. A grid structure as set forth in claim 5 in which at least certain of the projections on a bar have projecting lugs for engagement with an associated bar to assure minimum spacing of the bars relative to one another.

10. A grid structure as set forth in claim 5 in which said pipes are arranged vertically in a circle and in which the pipes are arranged in groups which are connected by said bars.

11. A grid structure as set forth in claim 10 in which there is a shield at and covering the upper ends of the pipes to deflect material dropped thereon, said shield having a generally circular periphery so that such material will drop into an annular pile around the pipes.

12. A grid structure as set forth in claim 10 in which each group of pipes has its own inlet and its own outlet,

9 and in which there is a common supply means connected to said inlets and a common discharge means for said outlets.

13. A grid structure as set forth in claim 5 in which at least certain of the bars are staggered relative to other 5 bars to tend to maintain a rigid predetermined spacing of the pipes.

14. A grid structure as set forth in claim 5 in which the pipes are arranged vertically in a circle, and in which certain pipes have upwardly and inwardly projecting extensions, and a cap structure disposed over and engaging said extensions.

15. A grid structure as set forth in claim 5 in which all the bars which engage any two pipes are mounted solely on said two pipes.

References Cited in the file of this patent UNITED STATES PATENTS 474,931 Whelen May 17, 1892 585,597 Sayer June 29, 1897 1,446,145 Allan Feb. 20, 1923 1,974,431 Priebe et a1 Sept. 25, 1934 10 2,883,973 Reagan Apr. 28, 1959 FOREIGN PATENTS 429,923 Great Britain June 5, 1935 

